Many of the optical memory disk systems in the related art have read/write heads that are relatively large and bulky for the desired performance characteristics of today's systems. Also such systems are quite expensive. A typical optical system head may have three or four lenses, a polarizing beam splitter, four prisms bonded together as a unit, and quarter-wave length plate, among other parts. Despite the disadvantages, such heads may have approximately 80 percent signal throughput.
In an effort to address some of the above-mentioned disadvantages, one company has developed a compact read/write optical head that incorporates a transmissive holographic element which replaces the beam splitter and some of the optical elements in the larger systems. The major components of this device are a laser diode, a solid state detector, and a holographic element. The immense disadvantage of this compact head is that the signal throughput is very low, that is, approximately one percent. Such a typical device is disclosed in U.S. Pat. No. 4,731,772, entitled "Optical Head Using Hologram Lens for Both Beam Splitting and Focus Error Detection Functions."